Is this a miscarriage.....

Few weeks ago I came on my period (late) in school and was in a lot of pain. This came out of me in the bathroom and I wrapped it up in a tissue because I didn't want to flush it just incase it was a miscarriage (hence why it's kinda stuck to the tissue) the bleeding was a lot heavier than usual and lasted two days with a lot of small clots, then about a week later I had a normal period. Is this just uterus lining or whatever it's called or is it what I think it is?